It's true that sacred scrolls would probably have a vested interest in name meanings for obvious reasons, but at the same time they're more focused on telling the sacred story than recording the etymological origins of names. Thus, name meanings can sometimes be suspect.
Tradition is just that: tradition. Folk etymology is very common--such as
Brendan's false meaning of "smelly hair"--and may easily be mistaken for true fact if nothing comes along to contradict it.
Miriam's meaning is probably truly unknown for sure (though, of course, it
does have a meaning; we just don't know what it could be!), and I bet folk etymology came along to fill in that gap of ignorance with a plausible origin or two. It could be correct, of course, but we have absolutely no idea whether it is or isn't.
In short, holy texts may or may not be reliable, and pious folk etymology shouldn't be blindly considered (pardon the pun) gospel.
Miranda
"Multiple exclamation marks are a sure sign of diseased mind" -- Terry Pratchett
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